Because fibroblast growth factor (FGF) signalling is important in many
developmental processes, its intensity and duration during embryogenesis must
be closely regulated. Tsang et al. reveal on
p. 2769 that
mitogen-activated protein kinase phosphatase 3 (MKP3) regulates the
FGF/RAS/MAPK signalling pathway through negative feedback in early zebrafish
embryos, and that this pathway helps to establish axial polarity. MKP3, whose
expression is controlled by FGF signalling through the RAS/MAPK pathway,
inhibits MAPK activity. The researchers show that the experimental alteration
of mkp3 expression disrupts dorsoventral patterning at gastrulation.
Endogenous mkp3 expression, they report, is initiated by a maternalβ
-catenin signal but its expression quickly comes under the control of
FGF signalling. These results indicate that the tight regulation of FGF
signalling, which the authors show here is necessary for specifying axial
polarity, is achieved by having MKP3 expression in place before FGF signalling
starts.